Fix process-based non-determinism in SparsePauliOp.to_matrix (backport #13439)
#13440
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* Fix process-based non-determinism in `SparsePauliOp.to_matrix` The simplification step of the summed Pauli terms in `SparsePauliOp.to_matrix` had introduced a non-determinism via hash-map iteration. In practice, the base hash seed was set per initialisation of the extension module, then stayed the same. This is hard to detect from within tests, but caused unexpected numerical behaviour on different invocations of the same script. * Use ahash::RandomState --------- Co-authored-by: Kevin Hartman <[email protected]> (cherry picked from commit 74b32c9)
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Changelog: Bugfix
Pull Request Test Coverage Report for Build 11842219577Details
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jakelishman
approved these changes
Nov 14, 2024
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Summary
The simplification step of the summed Pauli terms in
SparsePauliOp.to_matrixhad introduced a non-determinism via hash-map iteration. In practice, the base hash seed was set per initialisation of the extension module, then stayed the same. This is hard to detect from within tests, but caused unexpected numerical behaviour on different invocations of the same script.Details and comments
This fixes the bug part of #13413, but doesn't address the feature request. It should be eligible for backport to either 1.3.0 or 1.3.1, depending on whether there's time to make 1.3.0.
Writing a test that would exercise this would be pretty complex, so I haven't done it. I can if we feel strongly about it - we'd likely embed a little script into a test and spawn some
sys.executableinstances to run it and check the outputs all matched bit-for-bit.This is an automatic backport of pull request #13439 done by Mergify.